Think the notice outside was funny (6)
I believe the answer is:
amused
'funny' is the definition.
Both the answer and definition are adjectives. Perhaps you can see an association between them that I don't see?
'think the notice outside' is the wordplay.
'think' becomes 'muse' (to muse on something is to think about it).
'the notice' becomes 'ad' (both can mean an advertisement).
'outside' is an insertion indicator (some letters go outside others).
'muse' going inside 'ad' is 'AMUSED'.
'was' is the link.
Can you help me to learn more?
(Other definitions for amused that I've seen before include "Provoked mirth in" , "Queen Victoria wasn't!" , "happily occupied" , "Kept someone entertained" , "Medusa (anag)" .)